The latest Visual Studio 2019 preview, released yesterday, adds the vertical tabs layout option to the core product:
You can select it in options or right clicking a tab:
In the options you can now additionally select Alphabetical tab sorting (works only for vertical tabs).
There is a scroller when all tabs don’t fit and if the active tab is not visible in the list, its name is displayed in the top right corner:
If you organize several editor windows side by side, tab groups are displayed one below other:
Pinned tabs are displayed on the top and you can freely change tabs area width by dragging the separator:
Download Visual Studio Preview to try it for yourself.